Most species in these families are small, easily overlooked plants that live in damp forests, along rivers or on the branches
of other trees. However this was certainly not true of the lycopsids that lived during the Pennsylvanian. During the Pennsylvanian,
some lycopsids grew to be trees standing over 27 meters (90 feet) tall. Unlike most other plants, tree lycopsids appear to
have preferred places in the swamp that were flooded by water. When they died, their bark, wood, leaves and roots fell into
the swamp. Because of the high water level, the plant pieces did did not break apart completely. The bark, leaves and roots
of lycopsids were buried and over time became coal. As much as 70% of coal may be composed of the lycopsid plant parts.